/Engine/Plugins/Runtime/MassEntity/Source/MassEntity/Public/MassObserverManager.h
bool OnCompositionChanged ( const [FMassArchetypeEntityCollection](API\Plugins\MassEntity\FMassArchetypeEntityCollection) & EntityCollection, const [FMassArchetypeCompositionDescriptor](API\Plugins\MassEntity\FMassArchetypeCompositionDescrip-) & Composition, const [EMassObservedOperation](API\Plugins\MassEntity\EMassObservedOperation) Operation, [FMassProcessingContext](API\Plugins\MassEntity\FMassProcessingContext) * InProcessingContext )